Assessing the Knowledge of Students about Dental Bleaching in Shahid Bahonar University of Kerman, Iran

Statement of the Problem: An attractive smile and white teeth give self-confidence and provide impression of health, which help individuals for social and interpersonal success. Increasing demand for tooth bleaching and lack of relevant information on the other hand, necessitate a new investigation to assess the knowledge of the students about dental bleaching in Kerman. Purpose: This study was designed to assess the overall knowledge of the students of Shahid Bahonar University of Kerman regarding dental bleaching and their tendency to perform it. Materials and Method: This cross-sectional study enrolled 384 students who were selected by simple random sampling. A valid and reliable self-administered researcher-made questionnaire was employed to collect data about demographic information, health behavior, tooth bleaching, and the tendency to perform . This tool contained 8 questions with the focus on the knowledge of dental bleaching. Data were analyzed by using SPSS version 21 and regression analysis at a significant level of 0.05. Results: Overall, 59.55% of participants were male and 40.45% were female students. Most likely, the source for gaining information was internet. In this regard, 29 individuals were dissatisfied with tooth color, 27 ones with the appearance of teeth, 13.5% have done tooth bleaching, and 69% had tendency to do that. The preferred knowledge was about the difference between scaling and root planning (SRP) and bleaching. There was no significant difference between age, gender, and marital status variables with the knowledge of dental bleaching. Tooth color satisfaction increased the tendency to do bleaching about 1.87 times. Conclusion: The study highlights that 69 % of the students had a tendency to do the bleaching, their knowledge was moderate, and there was no statistical relationship between knowledge, gender, and marital variables. Color variable had an overall positive effect on the tendency to do the bleaching.


Introduction
People's appearance plays a key role in their social interactions; subsequently, the color of teeth is the most important determinant of patient satisfaction [1]. Recently, dental procedures have undergone changes especially in Western societies, because dental caries have been decreased, the numbers of remaining teeth have been increased, and the patients' demand for cosmetic dentistry is increasing [2][3]. The first report on tooth bleaching is cited in Zakaria Razi's Book of Al-Mansouri [4]. Feinman [5] developed the first bleaching method, using hot oxygenated water. Tooth bleaching in Iran started in 1335 at the School of Medicine and since then has been practiced by the Iranian dental schools [6].
Bleaching can be done with the use of carbamide peroxide, hydrogen peroxide, and sodium perborate with or without light activation. There are various techniques of vital bleaching, including bleaching in the office by high concentrations of bleaching materials with soft tissue protection or at-home bleaching by lower concentrations of bleaching materials [7][8][9]. Some negative effects such as nausea, tooth sensitivity, and gingivitis have been reported with the procedure [10][11][12][13].
Azodo and Ogbomo [14] and Mehl et al. [15] have reported that the arrangement and the size of teeth were important determinants of dental satisfaction for the Benin university students. Maghaireh et al. [16] found that 69.3% of patients were satisfied with the appearance of their teeth. However, Akarslan et al. [17] showed that among the patients referred to the dental School in Turkey, 55.1% were dissatisfied with tooth color and 42.7% with tooth appearance, while 29.9% of the patients were dissatisfied with tooth crowding and 23.3% of people concealed their teeth while smiling.
Samorodnitzky-Naveh et al. [18] highlighted that the main factor in tooth beauty was tooth color, although 37.3% of the patients were not satisfied with the appearance of their teeth. According to Subait et al. [19] among 238 students in Saudi Arabia, 15% of the students were dissatisfied with tooth appearance, 62% with tooth color, 62% of them had tendency to bleaching and 32% wanted to have orthodontic treatment.
Increasing demand for tooth bleaching and lack of a similar study in Kerman provide a new investigation to assess the knowledge of the students about dental bleaching in Shahid Bahonar University of Kerman.

Materials and Method
This descriptive-analytical cross-sectional study was conducted on the students of electrical, civil, industrial, chemistry, mechanics, metallurgy, computer and mining engineering, at Shahid Bahonar University of Kerman.
Data collection tool was a questionnaire that consisted of demographic information (gender, age, field of study, brushing frequency, dental flossing, and dental visits), some questions about tooth color satisfaction, importance of teeth appearance, tendency to do bleaching, history of dental bleaching and satisfaction, source of information, and eight questions about the knowledge of dental bleaching. The reliability and validity coeffi-cient of the questionnaire were 0.81 and 0.79, respectively, using ICC formula. Sample size was based on the below formula: n= (z^2*p(1-p)) /d^2, considering z= 1.96, d= 0.05 and p= 0.5, was calculated to be 400, but some questions had been missed by the respondents, thus final analysis was performed on only 384 questionnaires. After collecting the questionnaires, the data were coded and entered into SPSS statistical software version 21, using descriptive statistics tests (Mean, Standard deviation, frequency, and percentage of frequency). The independent t-test, chi-square and logistic regression test was performed at significant level 0.05.
The participants were assured that they would not be

Results
In this study, 59.55% of participants were male and 40.45% were female students (Table 1). In terms of oral hygiene behavior, 49.8% individuals brushed twice daily, 47% used dental floss and 35.3% had dental visits less than 6 months ago. In addition, 17.5% of the participants were reported to have smoking habit and 13, 5% were consuming hookah (Table 2).
Overall, 87% of people considered the appearance of teeth important and very important, whereas, 26.75% of the participants were dissatisfied and completely dissatisfied with the color of their teeth.
Only 44.33% of participants that had access to Internet presented more information on tooth bleaching and 14.09% gained their information by consulting their   al. [24], 32% by Nomay [21], and 26.6% by Subait et al. [19]. Their reported results were lower than the results yielded by our study (87 %), even though the tooth color may be the primary cause of dissatisfaction with tooth appearance [17].
In the current study, there was no statistically significant relationship between variables including gender, field of study, and age with dental color satisfaction.
According to Vallittu et al. [25], color satisfaction has been shown to be age-dependent. The results of the study by Akarslan et al. [17] indicated that people with higher degrees of education and higher self-esteem were more satisfied with the color of their teeth. The reason for the lack of statistical correlation between color satisfaction with age and education in this investigation is probably related to the same range of age, education level and being young middle-aged.
According to our study, there was no statistically significant relationship between dental appearance satisfaction with educational field, age, and gender, but Strajnić et al. [29] found that with increasing education level, satisfaction with the appearance of teeth was also increased. As such, in our study, five completely satisfied to completely dissatisfied question options were used to measure the degree of tooth color satisfaction.
This investigation shows that 13.5% of participants had done bleaching, while Hatherell et al. [30] revealed that 28.44% of the students had done bleaching, which was more than our study. This study also indicates that 69% of participants tended to do bleaching similar to that of Hatherell et al. [30], whereas 66.37% of students in the United Kingdom wanted to do tooth bleaching ( Table   3). The tendency to do bleaching in the Al-Zarea study [23] was, 80.9%, Akarslan et al. [17], 49% Tin-O-o et al. [31], 55.3%, Nomay [21], 77% and Subait 80% [19].
In the study of Maghaireh et al. [16], the most tendency for improving the appearance of teeth was tooth bleaching and it also was the most favorable treatment in Riyadh, London and Malaysia [19,[31][32].
In our study, female students were more likely to do bleaching, although the difference was not statistically significant. This can be attributed to the studied population and methods of assessing the tooth color satisfaction. In addition, 58.25% of students had heard about bleaching, but female students had significantly more hearing.
The main source of information in 44.33% of participants was Internet and the next levels were dentists, friends, and acquaintances ( Figure 2), which is somehow higher than the results (35.8 %) reported by Azodo et al. [14] in Nigeria. The reason for this difference may be due to greater access to the Internet in the current study.   There was no significant difference between participants' knowledge of dental bleaching in terms of gender and field of study. These results are not in line with Al-Nomay et al. study [21] that showed women were significantly more aware of the subject.
This study showed that 52.1% of students knew the difference between bleaching and SRP, even though our research had "no idea" option too (Table 4).
In addition, 25.9% of the students answered yes to the question of side effects of bleaching, which is less than 46 % reported by Diklić et al. [35]. Regression analysis showed that the tooth color satisfaction increased the odds of tendency for doing bleaching to 1.87 times. This may be due to the age range of the participants, the uniformity of their education, and appropriate health behavior. However, tooth color dissatisfaction can influence people's decision to do bleaching.
Despite the results of this study, the most confounding factors which affect the tendency to do bleaching, include the treatment cost, the long multiple visits for in-office bleaching, and tooth sensitivity with nausea after each visit of tooth bleaching. In addition, the participants of our study were at the same age range and education, which could be effective on our results.
Therefore, further investigations are needed concerning the knowledge and tendency of the public population to do dental bleaching.

Conclusion
The present investigation highlights that 35.5% of the subjects were satisfied with the color, 49.75% with the appearance of the teeth. Moreover, 69% had a tendency to do bleaching and the knowledge level about bleaching and its alternative treatments was moderate.